The control of switch-mode power supplies (SMPS) is increasingly moving to the digital domain. Digital control of power supplies allows for increased flexibility and robustness. For example, a digitally controlled and compensated power supply can be easily adapted for use in multiple electrical environments by reprogramming a digital compensation algorithm instead of changing or redesigning analog compensation networks. The use of such digital control and compensation can also save manufacturing costs and allow for sophisticated compensation schemes that may be difficult or impossible to implement in the analog domain.
In order to implement a digitally controlled power supply, an A/D converter is typically required. The inclusion of A/D converters in power supply systems, however can lead to higher material costs, integrated circuit area, test time and design effort. In power supply applications where multiple power supplies are being digitally regulated, multiple A/D converters may be used, or a single, high speed A/D with a multiplexed input can be used. Both of these solutions may lead to increased cost, silicon area, and power consumption.
A number of different A/D topologies have been proposed to for use in digitally controlled power supply systems. For example, a flash A/D can be used in a power supply system, but, the area and power consumption of a flash A/D may be prohibitive, especially in low-power power supply systems. A Successive Approximation A/D, on the other hand, may be more power efficient, but requires multiple clock cycles to perform each conversion, which makes it difficult to use with a multiplexed input at high per-channel sample rates.
What is needed are low-power, cost effective A/D converters that are well suited for use in power supply systems.